This invention relates in general to electrolysis and, more particularly, to the electrolysis of water into its constituent elements.
It is often desirable to decompose water into its chemical elements, namely hydrogen (H.sub.2) and oxygen (O.sub.2). Electrolysis is the chemical reaction typically employed to achieve this end. In a simple water electrolyzer, water is confined in a vessel in which a positive and negative electrode are situated. A direct current (DC) power supply is then coupled to the positive and negative electrodes. When the DC power supply is adjusted to a sufficiently high voltage, the water molecules break down and H.sub.2 gas is generated at the cathode while O.sub.2 gas is generated at the anode. In actual practice, the water in the vessel is a solution referred to as an electrolyte, for example a salt solution, which enables ionic conductivity between the electrodes. In the above described example, a liquid electrolyte is employed. Alkaline systems employing liquid electrolytes such as KOH and NaOH solutions are well known. These systems generally operate at relatively high temperatures such as 80 degrees C., for example.
Those skilled in the art are also familiar with the use of solid electrolytes in electrolyzers. For example, solid polymer electrolytes such as polystyrene sulfonates have been used and more stable perfluoroalkane sulfonate ionomers such as the Nafion ionomer (Nafion is a trademark of DuPont) have also been used.
In these days of energy conservation and great concern for efficiency, it is of course desirable that the maximum amount of H.sub.2 and O.sub.2 end products be obtained for a given power level applied to the electrolyzer. It is known that increasing the temperature at which electrolysis is conducted also increases the ionic conductivity across the solid polymer electrolyte membrane. Thus, the higher the temperature at which the electrolysis reaction is conducted, the lower are the drive voltage and drive power requirements for a given amount of H.sub.2 and O.sub.2 gas products.
Unfortunately, many solid polymer electrolytes exhibit relatively low conductivity at relatively low temperatures such as between approximately 20 through 70 degrees C. However, when many of such solid polymer electrolytes, such as Nafion for example, are subjected to higher temperatures such as 150 degrees C. and above to increase their ionic conductivity in an electrolytic reaction, their structural integrity comes into question. At high temperatures the glass transition temperature of many solid polymer electrolytes is approached and passed. In this case, the solid polymer electrolyte may begin to soften and flow thereby becoming structurally unstable. The solid polymer electrolyte may also break down into fragments and release undesired gaseous decomposition products.